The Wilms Tumor 1 (WT1) gene is a gene isolated as a gene responsible for Wilms Tumor, which is a pediatric renal tumor. In Wilms Tumor, deletion or mutation of the gene is found, and transfer of a normal WT1 gene into a cell line derived from Wilms Tumor inhibits cell growth. Accordingly, the WT1 gene has been considered to be a tumor suppressor gene. However, a later investigation has confirmed that a WT1 protein is highly expressed in leukemia and various types of solid tumor, and the WT1 gene is considered to serve a function of an oncogene rather than a tumor suppressor gene (Non Patent Literature 1: Jpn J Clin Oncol 2010; 40: 377-387).
Cancer immunotherapy started with LAK therapy based on innate immunity in the 1980s, and there have been performed: innate immunotherapy, such as NK cell therapy and treatment involving utilizing acquired immunity, such as peptide therapy involving targeting a peptide constituting a fragment of a protein serving as a cancer antigen; and dendritic cell vaccine therapy involving causing dendritic cells to recognize a cancer peptide and returning the cells into the body.
It has been confirmed that, when a mouse is immunized with a WT1 peptide, or when dendritic cells differentiated from human peripheral blood mononuclear cells are stimulated with a WT1 peptide, the WT1 peptide can be utilized as a dendritic cell vaccine capable of inducing WT1-specific cytotoxic T cells (CTLs). In addition, progress has also been made in clinical testing involving using the WT1 peptide. The related-art WT1 peptide is generated so as to be adapted to a certain human leukocyte antigen (HLA), and hence it has been necessary to identify an HLA allele of a patient by DNA typing (Patent Literature 1: JP 5714619 B2). In a later investigation, treatment of cancer using a complete sequence-type vaccine covering a complete sequence of the WT1 protein has been attempted. The vaccine is also applicable to patients of various HLA types. The vaccine also activates cancer antigen-specific CTLs and helper T cells that promote immune responses.
The most general administration route of the WT1 vaccine is subcutaneous or intradermal injection, but attempts have also been made to induce immunity by various administration routes other than the above-mentioned route, for example, transdermal administration and mucosal administration, such as buccal administration, nasal administration, and sublingual administration. However, no report has heretofore been made on oral administration.
A cell membrane is a biological membrane that separates the inside of the cell from the outside. On a surface of the cell membrane, there are a large number of membrane proteins each having a function of providing information on the cell or a function of transporting a substance endogenous or exogenous to the cell. The following concept has been proposed: a certain antigen is fused to a membrane protein so as to be displayed on a cell surface of a microorganism and be used as an oral vaccine for artificially inducing an antigen-antibody reaction. For example, there is known an example in which a vector having a gene encoding a membrane-binding portion of an enzyme protein, such as poly-γ-glutamate synthetase, is utilized to display a target protein on a cell surface of a host microorganism (Patent Literature 2: JP 2005-50054 A). In addition, with regard to a technology involving using, as a vaccine, a flagellin protein derived from a bacterium that causes an infectious disease, there is a report on an oral vaccine containing, as a capsule content, a transformed microorganism expressing flagellin (Patent Literature 3: JP 5187642 B2). In Patent Literature 3, it is reported that the transformed microorganism is prepared using, as the bacterium to be caused to produce flagellin, any of intestinal bacteria that are commonly referred to as good bacteria, such as microorganisms belonging to the genus Bifidobacterium (which are collectively referred to as “Bifidobacterium”) or lactic acid bacteria.
The Bifidobacterium is an indigenous bacterium found downstream in the small intestine of a human or other animals, or in the large intestine thereof. The Bifidobacterium is an obligately anaerobic Gram-positive bacterium, and hence has high selectivity in culture. Besides, the Bifidobacterium has high biocompatibility and does not have endotoxins, which are found in Gram-negative bacteria, and hence the Bifidobacterium is highly safe. Therefore, the Bifidobacterium has been GRAS-approved according to a standard of a review system regarding food safety. In addition, there is a report that the Bifidobacterium has a property of binding to mucus formed of mucin with which the intestinal tract is covered. Accordingly, the Bifidobacterium is considered to have a higher property of adhering to the intestinal wall than those of other bacteria in the intestines. There have already been developed and reported a technology for expressing and displaying a protein or a peptide on a surface of such Bifidobacterium, and a technology concerning a novel vaccine based on the Bifidobacterium, which uses the above-mentioned technology (Patent Literature 4: JP 5561681 B2).